Method and apparatus for surface grinding



United States Patent 3,277,609 METHOD AND APPARATUS FOR SURFACE GRINDING Imitaro Horie and Yozo Kimura, Kyoto, Japan, assignors to Tomohiro Horie, Kyoto, Japan Filed Feb. 7, 1964, Ser. No. 343,405 2 Claims. (Cl. 51-78) This invention relates to a method and apparatus for surface grinding metal sheets or plates using a grinding wheel composed of abrasive particles uniformly distributed in a polyvinyl acetal matrix or bond in order to achieve a more rapid and uniform surface finishing of the work piece than has heretofore been possible.

U.S. Patent No. 2,876,085, issued Mar. 3, 1959, to Tomohiro Horie, and entitled Process for Producing Grinding Materials, discloses a process for producing grinding materials and the products thereof, in which the abrasive particles are uniformly distributed in a spongy matrix consisting essentially of the reaction product of polyvinyl alcohol and formaldehyde or a material capable of releasing formaldehyde, which product is herein referred to as polyvinyl acetal. The present invention relates to a process and apparatus specially adapted for using a grinding wheel of this type.

It has previously been suggested to surface grind metallic plates, strips and sheets, especially steel strips fed from a coil in a variety of ways including using (1) endless abrasive belts, (2) buffing wheels, (3) Wire brushes, and (4) various other methods. The use of endless abrasive belts is not completely satisfactory because the belts wear out quickly due to erosion or dulling of the abrasive particles and because the belts stretch during use so the surface finish of the work pieces is not unifom. Bufiing wheels also wear out quickly due to dulling or erosion of the abrasive particles. Wire brushes leave deep scars or scratches on the polished surface which is undesirable. The other methods also are not completely satisfactory. For example, suggestions have been made to use a nylon fiber roll impregnated with abrasive grains but such a roll will not withstand the heat that is developed in the grinding operation. Rubber, wood or felt rolls having a grinding cloth or paper adhered thereto suffer from similar deficiences.

All of the known methods require that the grinding tool be resiliently mounted so that it can closely follow the shape of the surface being ground. This substantially complicates the design of the grinding machine and increases the cost thereof.

Accordingly, it is an object of this invention to provide an improved process and apparatus for grinding metal plates and sheets using a grinding wheel consisting essentially of abrasive particles uniformly distributed in a spongy polyvinyl acetal matrix.

It is a further principal object of this invention to provide a process and apparatus, as aforesaid, in which the grinding wheel is urged against the workpiece under a pressure within a critical pressure range and wherein the width of the zone of contact between the periphery of the grinding wheel and the workpiece lies within a specified critical area range, related to the diameter of the grinding wheel.

Other objects and purposes of the invention will become apparent to persons acquainted with grinding processes and equipment of this type upon reading the following disclosure and inspecting the accompanying drawings.

In the drawings:

FIGURE 1 is a schematic, perspective view of an apparatus for carrying out the invention.

FIGURES 2A, 2B and 2C are schematic views showing the position of the grinding wheel with respect to workpieces of varying shapes.

FIGURE 3 is a graph of the width of the contact zone vs. diameter of grinding wheel and the cross-hatched area thereof indicates the critical range of the width of the contact zone as related to the diameter of the grinding wheel which is an essential requirement of the present invention.

According to the invention, a cylindrical grinding wheel 1 consisting of abrasive particles uniformly distributed in a polyvinyl acetal matrix, said wheel being of more than millimeters in axial length, is used for surface grinding the metal strips, sheets and plates. The peripheral surface of the grinding wheel is pressed against the surface of the workpiece under a pressure of between about 1 and 6 kilograms per square centimeter while said grinding wheel is being rotated at a peripheral speed of between about 1500 to 2000 meters per minute and the workpiece is being moved substantially tangent to the periphery of the grinding wheel at a speed in excess of about 1 meter per minute and usually in a direction opposite to the direction in which the peripheral surface of the grinding wheel is being moved. The width of the contact zone between the workpiece and the grinding the following formula:

wherein L is the Width of the contact zone expressed in millimeters and D is the diameter of the grinding Wheel expressed in millimeters. Thus, the width of the contact zone related to the diameter of the grinding wheel must be within the cross-hatched area in FIGURE 3. Any value of L within the range set forth above can be used with any pressure within the range described above with satisfactory results.

The grinding wheel is formed in accordance with the procedures described in U.S. Patent No. 2,876,085 and such a wheel consists of a polyvinyl acetal spongy matrix having a multiplicity of independent pores connected with each other by capillary tubes. Suitable abrasive particles are mixed in and uniformly distributed throughout the polyvinyl acetal matrix.

Various types of abrasives can be used, such as silicon carbide, fused alumina, garnet, diamond bort, boron carbide, etc., and the abrasive particle size can range from 16 to 3000 mesh, depending upon the type of grinding operation to be performed. Similarly, the hardness and resiliency of the polyvinyl acetal matrix can be adjusted in order to meet various use requirements, such as by adding phenol-formaldeyhyde or urea-formaldehyde resin to the polyvinyl acetal molding mix. It will be understood that the grinding wheel may also comprise a centrally located hub, mounting flanges, bushings and the like for mounting the grinding wheel on a drive shaft but such can be of any conventional type and, hence, need no detailed description herein.

The contact pressure between the workpiece and the periphery of the grinding wheel is maintained between about 1 and 6 kilograms per square centimeter. If the pressure is below 1 kilogram per square centimeter, hardly any grinding will take place. It is believed that this is due to the resillency of the polyvinyl acetal matrix which permits the abrasive grains to press into the matrix, rather than being pressed uniformly against the workpiece. On the other hand, if the contact pressure exceeds about 6 kilograms per square centimeter, rapid wear of the grinding wheel will occur and the heat generated by the grinding operation will increase, which is undesirable for a variety of reasons, including the fact that it may cause deterioration of the polyvinyl acetal matrix. Also, higher pressures cause chattering of the wheel which is noisy and makes the surface finish of the workpiece less uniform.

It is of critical importance to the practice of this invention that the grinding wheel be at least about 100 millimeters in axial length, that is, in a direction along the axis of rotation of the wheel, because it has been found that wheels of lesser axial length do not elfectively surface grind the workpieces uniformly to a smooth surface finish. It is believed that this is due to the fact that the grinding pressure is not distributed over the workpiece as uniformly as is necessary. Similarly, it is of critical importance to move the workpieces at a rate in excess of about 1 meter per minute in a direction substantially tangent to the grinding zone. At lower speeds the surface of the workpiece becomes unacceptably roughened and irregular. Usually the workpiece is moved in a direction opposite to the direction of movement of the periphery of the grinding wheel.

The workpieces ground according to the invention can be of flat, curved or irregular shapes so long as the grinding wheel can contact same uniformly over substantially its entire axial length. Since the polyvinyl acetal matrix is resilient, some deformation thereof will occur under the grinding pressure so that the workpiece and the periphery of the grinding wheel Will be in contact with each other over a zone of appreciable width. In order to obtain a uniform grinding of the surface of the workpiece, the width of the contact zone must fall within the critical range referred to previously.

Because the polyvinyl acetal matrix provides a substantially even, resilient resistance, there is less heat generated in the grinding operation and the creation of localized hot spots in the wheel or on the workpiece is substantially eliminated. The polyvinyl acetal matrix can yield as needed to compensate for minor irregularities in the grinding wheel and/or the workpiece so that an even surface treatment of the workpiece results. It is to be noted that the procedure of the invention brings a large number of abrasive grains into contact with the workpiece concurrently and at a uniform pressure so that the grinding will take place uniformly. Moreover, because the cutting angle of individual abrasive particles with respect to the workpiece can change by resilient yielding of the polyvinyl acetal matrix, the cutting quality is excellent and formation of sharp or rough edges on the work piece is avoided.

The method of the invention can be used for wet or dry grinding.

FIGURE 1 illustrates an apparatus capable of carrying out the invention and such apparatus includes a grinding wheel 1, constructed as aforesaid, which is radially aligned with a backup roll 2. In this embodiment, the axis of the grinding Wheel 1 is not movable toward and away from the Work piece W but the axis of the backup roll 2 is connected by a linkage arrangement 3 to the ram 4 of a cylinder 5 so that by supplying fluid under a suitable pressure to the cylinder 5, the backup roll 2 will be urged upwardly against the periphery of the grinding wheel 1 under a suitable controllable pressure in order to achieve a contact pressure within the range set forth above. The work piece W is fed through a pair of feed rolls 6 into the bite of the grinding Wheel 1 and the backup roll 2 and thence passes outwardly therefrom through the takeoif rolls 7. Either or both of the feed rolls 6 and the takeoff rolls 7 can be driven, as if needed, or other drive means can be provided to move the workpiece W with respect to the grinding wheel 1 at a rate in excess of about 1 meter per minute, as above described.

The invention will be further described with reference to specific examples but it is to be understood that such examples are given for illustrative purposes only and that the invention is not limited to the specific features thereof.

Example 1 Finish polishing of a stainless steel strip after cold annealing grinding conditions:

(1) Dimensions of workpiece 0.3 mm. thick x 110 mm. wide x 300 meters long.

(2) Grinding wheel used: Size-500 mm. in diameter x 110 mm. in width. The grinding Wheel consisted of 35% by volume of abrasive grains, 10% by volume of polyvinyl acetal matrix, the remainder of the volume consisting of pores having an average diameter of about 0.3 mm.

(3) Speed of grinding wheel--l200 rpm.

(4) Velocity of stainless steel strip6 meters per minute.

(5) Pressure of grinding wheel4 kilograms per square centimeter.

(6) Width of contact zone-20 mm.

It was found that by surface grinding the stainless steel strip under the above mentioned conditions, an improved surface finish was formed at a much higher rate than had been accomplished hitherto.

Example 2 Mirror polishing of magnesium sheets grinding conditions:

(1) Dimension of workpiece-1.2 mm. thick x 500 mm.

wide x 10 meters long.

(2) The grinding wheel had a diameter 400 millimeters and was 510 millimeters in axial length. The grinding wheel consisted of 28% 'by volume of abrasive grains, 12% by volume of polyvinyl acetal matrix and the remainder of the grinding wheel was pores having an average diameter of 0.2 mm.

(3) Speed of rotation of grinding wheellSOO rpm.

(4) Velocity of magnesium sheets-5 meters per minute.

(5) Grinding pressure-l kilogram per square centimeter.

(6) Width of contact zonel2 mm.

It was found that by comparison with the prior art practices of polishing magnesium sheets by bufiing, sand paper or charcoal, the procedure of the present invention provides a better surface finish in much less time than the prior art practices.

The width (L) of the contact zone will depend upon a number of factors including the pressure exerted to urge the workpiece against the grinding wheel, the compressibility of the grinding wheel, the speed of rotation of the grinding wheel and perhaps others. However, in any given installation the width of the contact zone ordinarily is changed by adjusting the pressure exerted to urge the workpiece against the grinding wheel, such as by adjusting the fluid pressure applied to the cylinder 5. The contact pressure at all times is maintained within the range described above.

While particular preferred embodiments of the invention have been described, the invention contemplates such changes or modifications therein as lie within the scope of the appended claims.

What is claimed is:

1. A method of surface grinding metal plates and sheets which comprises pressing the peripheral surface of a rotating grinding wheel consisting essentially of abrasive particles uniformly distributed in a spongy polyvinyl acetal matrix and of more than mm. in axial length against the surface of a workpiece which is being moved at a speed in excess of one meter per minute, in a direction substantially tangent to the periphery of the grinding Wheel, the contact pressure of the grinding wheel against the workpiece being between about 1 and 6 kilograms per square centimeter and the width of the contact zone between said periphery and the surface of the workpiece being within the range:

wherein L is the width of the contact zone in millimeters, and D is the diameter of the grinding wheel in millimeters. 2. An apparatus for surface grinding metal plates and sheets comprising:

a rotatable grinding wheel consisting essentially of abrasive particles uniformly. distributed in a spongy polyvinyl acetal matrix, said grinding wheel being of at least 100 mm. in axial length;

backup means associated with said grinding wheel and radially aligned therewith and means for urging said backup means and grinding wheel toward each other 5 under a pressure of between about 1 and 6 kilograms per square centimeter;

and means for feeding a workpiece between said grinding wheel and said backup means.

References Cited by the Examiner UNITED STATES PATENTS 1,995,382 3/1935 Fenton 51-78 X 2,340,121 1/1944 Hamilton 51-78 2,876,085 3/1959 Horie 51-2196 LESTER M. SWINGLE, Primary Examiner. 

2. AN APPARATUS FOR SURFACE GRINDING METAL PLATES AND SHEETS COMPRISING: A ROTATABLE GRINDING WHEEL CONSISTING ESSENTIALLY OF ABRASIVE PARTICLES UNIFORMLY DISTRIBUTED IN A SPONGY POLYVINYL ACETAL MATRIX, SAID GRINDING WHEEL BEING OF AT LEAST 100 MM. IN AXIAL LENGTH; BACKUP MEANS ASSOCIATED WITH SAID GRINDING WHEEL AND RADIALLY ALIGNED THEREWITH AND MEANS FOR URGING SAID 